The present invention relates to wavelength division multiplexers and de-multiplexers in optical communications networks and systems. More particularly, the present invention relates to such multiplexers and de-multiplexers that employ diffraction gratings to spatially disperse wavelength multiplexed channels of arbitrary wavelength spacing and band width according to their respective wavelengths.
Fiber optic communication systems are becoming increasingly popular for data transmission due to their high speed and high data capacity capabilities. Wavelength division multiplexing is used in such fiber optic communication systems to transfer a relatively large amount of data at a high speed. In wavelength division multiplexing, multiple information-carrying signals, each signal comprising light of a specific restricted wavelength range, may be transmitted along the same optical fiber.
In this document, these individual information-carrying lights are referred to as either xe2x80x9csignalsxe2x80x9d or xe2x80x9cchannels.xe2x80x9d The totality of multiple combined signals in a wavelength-division multiplexed optical fiber, optical line or optical system, wherein each signal is of a different wavelength range, is herein referred to as a xe2x80x9ccomposite optical signal.xe2x80x9d
The term xe2x80x9cwavelength,xe2x80x9d denoted by the Greek letter xcex (lambda) is used herein synonymously with the terms xe2x80x9csignalxe2x80x9d or xe2x80x9cchannel,xe2x80x9d unless it is used in the expression xe2x80x9cphysical wavelength,xe2x80x9d wherein it retains its usual meaning. Although each information-carrying channel actually comprises light of a certain range of physical wavelengths, for simplicity, a single channel is referred to as a single wavelength, xcex, and a plurality of n such channels are referred to as xe2x80x9cn wavelengthsxe2x80x9d denoted xcex1-xcexn. Used in this sense, the term xe2x80x9cwavelengthxe2x80x9d may be understood to refer to xe2x80x9cthe channel nominally comprised of light of a range of physical wavelengths centered at the particular wavelength, xcex.xe2x80x9d
Strictly speaking, a multiplexer is an apparatus which combines separate channels into a single wavelength division multiplexed composite optical signal and a de-multiplexer is an apparatus that separates a composite optical signal into its component channels. However, since many multiplexers and de-multiplexers ordinarily operate in either sense, the single term xe2x80x9cmultiplexerxe2x80x9d is usually utilized to described either type of apparatus. Although this liberal usage of the term xe2x80x9cmultiplexerxe2x80x9d is generally used in this specification, the exact operationxe2x80x94either as a multiplexer or a de-multiplexerxe2x80x94of any particular apparatus should be clear from its respective discussion.
A crucial feature of fiber optic networks is the separation of the composite optical signal into its component wavelengths or channels, typically by a wavelength division de-multiplexer. This separation must occur to allow for the exchange of signals between loops within optical communications networks. The exchange typically occurs at connector points, or points where two or more loops intersect for the purpose of exchanging wavelengths. Conventional methods utilized by wavelength division de-multiplexers in separating a composite optical signal into its component channels include the use of filters and fiber gratings as separators. A xe2x80x9cchannel separatorxe2x80x9d, as used in this specification, is an integrated collection of optical components functioning as a unit which separates one or more channels of a composite optical signal from one another.
Frequently, wavelength division multiplexed fiber-optic communications systems may simultaneously carry different types of data trafficxe2x80x94for example, the simultaneous transmission of voice communications, computer data and video signals. The different types of data generally comprise different data transfer rates. The different data transfer rates are associated with different bandwidth requirements in the fiber-optic communication system. For instance, voice communications involve relatively slow data transfer rates and, consequently, consume relatively little bandwidth. Such low-rate communications can be constrained to low-bandwidth channel slotsxe2x80x94that is, they can be allocated to channels occupying relatively small bandwidthxe2x80x94without adverse effects. On the other hand, video communications involve large data transfer rates and therefore consume greater bandwidth. Such communications must be allocated to channels of appropriately wider band width. Finally, computer data are often transmitted through fiber optic and other networks utilizing the well-known SONET protocol. The speed of data transmission depends upon the particular data transmission protocol used by the SONET transmitters and receivers. For instance, data transfer adhering to the OC-48 protocol is transmitted at 2.5 GBit/s whereas data transfer utilizing the OC-192 protocol is transmitted at 10 GBit/s. If such protocols are mixed over a single fiber, they will occupy different natural bandwidths.
The overall available bandwidth of a wavelength-division multiplexed optical fiber system may be utilized most efficiently when the various data streams are allocated to channels comprising bandwidths appropriate to or matched to their respective data transfer rates. This type of allocation necessitates uneven or asymmetric.channel spacing and non-uniform bandwidths. Otherwise, as is conventionally done, all channels must be assigned to a regular spacing and uniform bandwidth. This conventional channel assignment scheme is wasteful of bandwidth when different signal types or protocols are transmitted simultaneously, since all channels must be allocated a bandwidth corresponding to the highest data rate transfer.
Accordingly, there exists a need for an asymmetric channel separator. The separator should separate or combine optical channels comprising arbitrary spacing and non-uniform bandwidths so as to overcome the above mentioned limitations of conventional channel assignment schemes. The present invention addresses such a need.
An asymmetric de-multiplexer/multiplexer includes: at least a first, second, and third optical fibers; at least one lens optically coupled to the first, second, and third optical fibers; at least one diffraction grating optically coupled to the at least one lens at a side opposite to the first, second, and third optical fibers; and a reflector array optically coupled to the at least one lens at a side opposite to the at least one diffraction grating. The reflector array includes: a substrate, and a plurality of reflectors coupled to the substrate at a side opposite to the at least one lens, where the plurality of reflectors reflects a first subset of channels of a composite optical signal traversing the apparatus, where the subset of channels has irregular inter-channel spacings and non-uniform bandwidths. The apparatus thus is able to overcome bandwidth utilization inefficiencies of conventional regular spaced channel assignment schemes.